Support FTP with implicit TLS without certificate validation

[grvoicu]

Why

We want to support various providers.

What

• BOTS able to retrieve files from a FTP server with implicit TLS, with a self-signed certificate

Notes

• Command-line connection to the server from the docker container was successful https://unix.stackexchange.com/questions/71525/how-do-i-use-implicit-ftp-over-tls.
• Relevant code:

  bots/src/bots/communication.py

  Line 1421 in 0d955b5

  class ftpis(ftp):

[radu-tutueanu]

This is needed for FTP with TLS, not SFTP